i386: introduce hv_cpuid_cache

i386: introduce hv_cpuid_cache

Just like with cpuid_cache, it makes no sense to call
KVM_GET_SUPPORTED_HV_CPUID more than once and instead of (ab)using
env->features[] and/or trying to keep all the code in one place, it is
better to introduce persistent hv_cpuid_cache and hv_cpuid_get_host()
accessor to it.

Note, hv_cpuid_get_fw() is converted to using hv_cpuid_get_host()
just to be removed later with Hyper-V specific feature words.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20210422161130.652779-9-vkuznets@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>